Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to absorbent pads such as disposable
diapers and the like for use in contact with the skin and pertains more
specifically to a top sheet (or face sheet~ for use in such absorbent pads
providing greatly improved dryness properties with little or no increase
in strike through time.
Absorbent pads such as disposable diapers customarily comprise a
water-resistant backing sheet, a layer of absorbent material, and a liquid
pervious top sheet (or face sheet), the top sheet being arranged to be placed
in contact with the body or skin of an individual.
Important characteristics of the top sheets of such absorbent
pads are that they delay or minimize passage of aqueous liquid such as urine
from the layer of absorbent material, after saturation, through the top
sheet to the external surface thereof (i.e., that they and the pads of which
they form a part exhibit high "dryness"), while at the same time they pro-
vide fast initial passage of an aqueous liquid such as urine from outside
the pad in the reverse direction through top sheet into the layer of absor-
bent material (i.e., that they and the pads of which they form a part
exhibit short "strike through" time). In addition, it is highly desirable
that top sheets of such absorbent pads be flexible and possess a soft hand,
and that they exhibit acceptable strength when they are wet.
In the past it has been customary to provide top sheets in the
form of one or more non-woven fibrous webs of textile fibrous material such
as polyester, rayon, polyamide, polypropylene or the like fibers together
with a binder of water insoluble polymeric material serving to bond the
fibers together, and to ensure adequate dryness properties by employing a
top sheet of high weight,
The present invention relates to an improved disposable diaper
having a water-resistant backing sheet, a layer of absorbent material, and
a top sheet arranged to be placed in contact with the skin, the improvement
~0 comprising a top sheet having a fibrous textile web impregnated with a
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polymeric binder in which at least 1% by weight of the binder con-
sists of combined 2-ethyl hexyl acrylate.
It has now been found that the dryness of such top
sheets and of absorbent pads in which they are present is signi-
ficantly improved by including in the polymeric binder composition
at least 1%, by weight of the total polymeric binder, of combined
2-ethyl hexyl acrylate, preferably from 3 to 30% by weight. The
combined 2-ethyl hexyl acrylates may be present as a homopolymer
which is mixed with the remaining polymeric binder, or it may be
present as a copolymer of 2-ethyl hexyl acrylate with one or
more other polymerizable monomers containing a polymerizable
ethylenic unsaturation. Consequently the binder may include
simply a single copolymer of 2-ethyl hexyl acrylate with one or
more other copolymerizable ethylenically unsaturated monomers,
or it may include a mixture of such a copolymer with one or
more other polymers or copolymers of other polymerizable ethy-
lenically unsaturated monomers, or it may include a mixture of
a homopolymer of 2-ethyl hexyl acrylate with one or more homo-
polymers or copolymers of other polymerizable ethylenically
unsaturated monomers, provided that the total weight of combined
2-ethyl hexyl acrylate amounts to at least 1% of the total weight
of polymeric binder, preferably from 3 to 30% by weight.
Among the preferred other polymerizable ethylenic
monomers with which 2-ethyl hexyl acrylate can be copolymerized
are lower alkyl acrylates in which the alkyl groups contain 1
to 5 carbon atoms such as ethyl acrylate or butyl acryla*e, vinyl
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acetate or vinyl propionate, acrylonitrile, vinyl chlorlde,
styrene, acrylic or methacrylic acid, or the like. The same
polymerizable ethylenic monomers can be homopolymerized or
copolymerized with each other and mixed with a homopolymer or
copolymer of 2-ethyl hexyl acrylate to form a blnder suitable for
use in the present invention. It is preferred when a homopolymer
or copolymer of 2-ethyl hexyl acrylate is blended with a conven-
tional polymer or copolymer (free from 2-ethyl hexyl acrylate) to
form the binder, that the first homopolymer or copolymer contain
at least 50~ by weight of combined 2-ethyl hexyl acrylate. I~hen a
copolymer of 2-ethyl hexyl acrylate with another copolymerizable
ethylenic monomer is used as the sole polymer in the binder, it
is preferred that it contain at least 1% of combined 2-ethyl hexyl
acrylate. In one preferred embodiment the polymeric binder
comprises a copolymer of an alkyl acrylate in which the alkyl
group contains from 1 to 5 carbon atoms with 2-ethyl hexyl
acrylate. In another preferred embodiment the polymeric binder
comprises a copolymer of an alkyl acrylate in which the alkyl
group contains from 1 to 5 carbon atoms with vinyl acetate and
with 2-ethyl hexyl acrylate. In other preferred embodiments the
polymeric binder comprises a copolymer of butyl acrylate or of
a mixture of butyl and ethyl acrylate with vinyl acetate and with
2-ethyl hexyl acrylate. The total polymeric binder present in
the top sheet is at least 15~ by weight of the entire top sheet
including the fibrous web, preferably from 20 to 50% by weight of
the total top sheet. The total top sheet weighs from 10 to 30
grams per square yard.
In the drawing,
Fig. 1 is a plan view of a disposable diaper embodying
0 a top sheet of the present invention; and
352
Fig. 2 is a view in section partly broken away taken
along line 2-2 of Fig. 1.
As shown in the drawing, the disposable diaper includes
a top sheet 10, a layer of absorbent material 12, and water
resistant backing sheet 14, sheets 10 and 14 being bonded together
around the periphery of the diaper in the usual manner. Any
conventional layer of absorbent material can be used, as well as
any conventional water resistant backing sheet.
The top sheet 10 in the present invention comprises one
or more webs of any natural or synthetic textile fibers such as
rayon, polyamide, polyester, polypropylene, or the like, polyester
fibers being preferred; along with the web is emploved a polymeric
binder composition containing at least 1% by weight of combined
2-ethyl acrylate. The combined 2-ethyl hexyl acrylate can
be present in the form of a homopolymer or ln the form of a
copolymer with other monomers containing polymerizable ethylenic
unsaturation, as described above.
The dryness and strike through characteristics of the
top sheet of the present invention and of the absorbent pads
incorporating it are measured by conventional test procedures
well known to those skilled in the art. To determine strike
through time, a sample of the top sheet to be tested is placed on
top of a layer of absorbent material, and a measured amount of
synthetic urine solution (20 g solium chloride and 5 g of octyl
phenoxy polyethoxy (9-10) ethanol sold as Triton*X-100 dissolved
in 1990 ml of water) is deposited on top of the top sheet, and
the time required for the solution to pass through the top sheet
is measured. After measuring the strike through time, additional
*Trad~mark
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352
measured amounts of the solution are passed through the top sheet
into the layer of absorbent material. A weight of 8 lb. is then
placed on the upper surface of the top sheet for 3 minutes, after
which the weight is removed. Two pieces of filter paper of known
weight are placed on the upper surface of the top sheet, the
weight is replaced and allowed to remain for 2 minutes. The two
pieces of filter paper are then removed and weighed to determine
the amount of solution absorbed by the filter paper. This amount
is defined as the dryness value of the top sheet.
Examples
In all examples, the fiber webs were made by carding
polyester fibers into a web of 4-5 g/yd2 weight. By combining
three of such webs on a conveyor belt, a total web weight was
obtained between 12 and 14 g/yd . This combined web was then
saturated by passing the web through the nip of a gravure print
roll and a rubber press roll. The gravure print roll, by
rotating in a bath of formulated latex, delivers a controlled
amount of binder to the fibrous web.
After passing through the nip of the print roll and the
rubber rcll, the saturated web was then dried for approximately
60 seconds at 320F. In each case the finished top sheet contained
approximately 65% by weight of polyester fibers and approximately
35% polymeric binder, the total weight of the sheet being 18-20
g/sq. yd.
Before testing, all fabrics were conditioned for at
least one hour at 70F and 65% RH.
The latex formulation used as a control or standard
was an aqueous dispersion containing about 15% by weight of a
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binder copolymer consisting of approximately 42~ combined butyl
acrylate and approximately 52% combined vinyl acetate by weight
along with small amounts of N-methylol acrylamide and of acrylic
acid; the dispersion also contained minor proportions of con-
ventional emulsifying agents and of ammonlum chlorlde. Slmllarproducts were prepared in the same way except that the aqueous
dispersion of binder copolymer contained in addltlon varying
amounts ofabinder copolymer as described in U.S. Patent 3,299,010
contalnlng comblned thereln 65 parts by welght of 2-ethyl hexyl
acrylate, 27.5 ethyl acrylate, 2.5 acrylonltrile, 1.0 acryllc
acid and 4.0 Primene maleamic acid. The amounts of the second
copolymer were such that the amounts of comblned 2-ethyl hexyl
acrylate ln the total polymeric blnder were as shown ln the
followlng table, the total binder in each case being approximately
35~ by weight of the total sheet. The dryness of each top sheet as
determined by the standard test described above was as shown ln
the table.
Table I
Percent comblned 2-ethyl
hexyl acrylate ln total binder 0 0.65 3.25 6.5
Dryness (g) 0.84 0.72 0.34 0.20
Strlke through (sec) 1.3 1.0 1.3 1.3
Other top sheets were prepared uslng the same procedure
by adding to the control latex a copolymer latex containing in
combined form 75 parts by welght 2-ethyl hexyl acrylate, 20 ethyl
acrylate, 2.5 methyl acrylate, 2.5 acryllc acld and 2.25 of a
monomer consisting of the mole to mole reaction product of malelc
anhydride, dlmethyl amlno ethanol, and chloracetamlde, wlth whlch
reactlon product is mlxed an equimolar amount of ammonium lauryl
sulfate. The latter combination of monomer with ammonium lauryl
sulfate serves as a dispersing agent for all of the monomers as
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well as for the finished polymer of which it forms a part, as
described in Samour U.S. Patent No. 3,925,442. The amounts of
combined 2-ethyl hexyl acrylate in the total polymeric binder and
the strike through and dryness of each top sheet were as follows:
Table II
% combined 2-ethyl hexyl
acrylate in total binder 0 0.73 3.67 7.3 14.7
Dryness (g) 1.17 .97 .10 .10 .10
Strike through (sec) 1.0 1.1 1.1 1.2 5.9
Still other sheets were made by adding to the control
latex a copolymer latex having in combined form 80 parts by
weight 2-ethyl hexyl acrylate, 15.5 parts ethyl acrylate, 2.5
parts acrylonitrile, and 2.0 parts acrylic acid, and containing
as a dispersing and stabilizing agent an alkylated bisulfonated
diphenyl ether. The amounts of combined 2-ethyl hexyl acrylate
in the total polymeric binder and the strike through and dryness of
top sheets were as follows:
Table III
% combined 2-ethyl hexyl
acrylate in total binder 0 0.8 4.0 8.0
Dryness (g) 1.0 0.33 0.22 0.14
Strike through (sec) 1.0 1.2 1.1 2.8
Other sheets were made, using the same procedures, by
impregnating a polyester fiber web with different polymeric
binders consisting solely of a copolymer containing butyl
acrylate (BuAcr), vinyl acetate (VAc), 2-ethyl hexyl acrylate
(2 EHA) and minor quantities of N-methylol acrylamide (N~A) and
acrylic acid (AA), the latter two being the same for all
copolymers, with results as shown in the following table:
13S2
.. . . . . .. . .. . .. .. .. . ..
42 parts BuAcr 38 parts BuAcr 35 parts BuAcr
Copolymer 52 parts VAc , 47 parts VAc 43 parts VAc
Composltion
Small amounts Small amounts I Small amounts
of NMA and AA I of NMA and AA I of NMA and AA
0 parts2 EHA '9 parts 2 EHA 17 parts 2 EHA
!
Weight (g/yd2)~ 19.5 ~18.5 ~ 17.8
of sheet
Strike through~ i ~
(sec) 1.4 ~1.8 i1.8
L Dryness (g)1.6 ~1.0 ~0.6
Other sheets were made by impregnating a polyester
fiber web with binders that are copolymers of ethylacrylate
(Ethylacr.), 2-ethyl hexyl acrylate (2-EHA) and minor quantities
of acrylic acid (AA) and N-methylol acrylamide (NMA), the latter
two being the same for both copolymers, with results as set forth
in the following table:
I 92 parts Ethylacr ¦ 80 parts Ethylacr
i Composition 1~ Small amounts of Small amounts of
of AA and NMA AA and NMA
Copolymer ~
No EHA 15 2-EHA
Weight (g/yd2) 17.8 18.8
Strike through I
(sec) ~ .98 3.5
Dryness (g) ~ .47 .16
Similar results can be obtained by employing other
polymeric binders containing amounts of combined 2-ethyl hexyl
acrylate within the range specified above.
